1. Field of the Invention
The present invention relates to a hydrodynamic pressure bearing, and more particularly, to a hydrodynamic pressure bearing enabling to repeatedly circulate fluid for generating hydrodynamic pressure therein.
2. Description of the Related Art
A hydrodynamic pressure bearing serves to generate the driving force of a spindle motor being installed in a hard disk driver and the like. One of examples, Japanese Patent Registration No. 2,937,833 discloses ┌Bearing seal system┘, which is illustrated with reference to FIGS. 3 and 4.
As shown, the bearing seal system is composed of a shaft 31 and a radial bearing section 24.
The radial bearing section 24 is arranged on the shaft-orientations outside, and provided with a clearance change section 50 for preventing leakage of the oil 15 present between the bearing section 24 and the shaft 21. Also, an oil surface section 15a of the oil 15 filled up the cylinder-like bag part 40 is set up to be located in the clearance change section 50.
The clearance change section 50 has a clearance change circles edge 50a set as the shaft-orientations most inner edge by the side of the radial bearing 24 and a clearance change section outer edge 50b set as the outermost edge of the clearance change section 50. The clearance change circles edge 50a is smallest and the clearance change section outer edge 50b is largest, and also a clearance tilt angle α is made therebetween.
Although the inner capacity of the bag part 40 is not constant during manufacturing or injection of the oil 15, the inner capacity of the bag part 40 is changed by the rise of the shaft 31 or heat due to the rotation of the shaft 31, or the change of the amount of the oil 15 due to the inner mixed air is raised, the constant amount of oil 15 will always be kept in the bearing section 24 without leakage since the inner capacity of the clearance change section 50 is relatively greater than the inner capacity of the bag part 40 or radial bearing section 24.
However, the sealing system described above has a drawback that may not keep the oil in the bag part 40 and then raise oil leakage if variation of conditions such as viscosity of oil or heat generated by the rotation of the shaft and the like exceeds the design criteria thereof.